The interscalene block is most applicable to shoulder repairs, in contrast to forearm and hand surgical procedures, although some practitioners combine interscalene and axillary blocks to produce an approximation of a supraclavicular block. When undertaking a block for shoulder surgery that requires muscle relaxation, a local anesthetic concentration that provides adequate motor block should be chosen (i.e., mepivacaine and lidocaine at 1.5%, bupivacaine at 0.5%, or ropivacaine at 0.75%). Because this block is most often carried out through a single injection site and the operator relies on the spread of local anesthetic solution, one must allow sufficient “soak time” after the injection, which is often 20 to 35 minutes.

If there is difficulty identifying the anterior scalene muscle, one maneuver is to have the patient maximally inhale while the anesthesiologist palpates the neck. During this maneuver the scalene muscles should contract before the sternocleidomastoid muscle contracts, which may allow clarification of the anterior scalene muscle in the difficult-to-palpate neck. Furthermore, if one is finding it difficult to elicit a paresthesia or produce a motor response during nerve stimulation with this block, it is almost always because the needle entry site has been placed too far posteriorly. For example,
Figure 4-6
shows that if the right side of the neck is divided into a 180-degree arc, the needle entry site should be approximately 60 degrees from the sagittal plane to optimize the block.

Figure 4-6 Interscalene block anatomy: an angle of approximately 60 degrees from the sagittal plane optimizes the needle angle for the block.

Most of the injection difficulties that result in complications of the block can be avoided if one remembers that it should be an extremely “superficial” block; if the palpating fingers apply sufficient pressure, no more than 1 to 1.5 cm of the needle should be necessary to reach the plexus. It is when the needle is inserted deeply that one must be cautious about subarachnoid, epidural, and intravascular injection. If one is planning to use the interscalene block for an operation that requires ulnar nerve block, I emphasize that this would not be my choice for a brachial plexus block with such a procedure. The ulnar nerve is difficult to block with the interscalene approach because it is derived from the eighth cervical nerve (this nerve is difficult to block after injection at a more cephalic injection site). Finally, one should be cautious about using this block in a patient with significant pulmonary impairment, as phrenic block is almost guaranteed with the interscalene block.